Angiotensin II and prostaglandin E2 play an important role in the regulation of blood pressure in normal and hypertensive animals. The actions of these hormones are mediated via their interaction with specific plasma membrane hormone receptors. The effect of these hormones on blood pressure is dependent upon the plasma concentration of the hormone as well as the affinity and density of the hormones receptor. Renomedullary interstitial cells have both angiotensin and prostaglandin receptors and are to be studied as a model of the vascular angiotensin and prostaglandin receptors. The following experimental studies will be performed: 1. In Vitro Characterization of the Prostaglandin Receptor of the Rabbit and Rat Renomedullary Interstitial Cell - prostaglandin binding will be studied using cells in tissue culture with respect to the effects of pH, cations and osmolality; down-regulation in response to receptor occupancy by PGE2 will be investigated. 2. In Vitro Regulation of the Angiotensin Receptor - down regulation of the angiotensin receptor after incubation with angiotensin II or saralasin will be determined. 3. In Vivo Regulation of the Angiotensin and Prostaglandin Receptors - using plasma membranes prepared from autologous renomedullary interstitial cell explants in rats, angiotensin and PGE2 receptor affinity and density and angiotensin-stimulated phospholipase activity and PGE2 - stimulated adenylate cyclase will be determined in response to a) changes in dietary sodium or potassium intake; b) infusions of angiotensin II, saralasin, or inhibitors of converting enzyme; c) nephrectomy; d) prostaglandin synthesis inhibition, PGE2 infusion, or the infusion of a prostaglandin receptor antagonist. In addition the renomedullary interstitial cells of spontaneously hypertensive, DOCA-salt hypertensive, and renal artery stenosis hypertensive rats will be studied.